The present invention relates generally to an adjustable antenna bracket. More particularly, the present invention relates to an adjustable antenna bracket readily attachable to a pole such as a wooden utility pole or electric transmission tower, or to a building roof top, for simultaneously adjustably mounting a plurality of antennas relative to each other, relative to other antenna sites, and plumb with the earth.
All wireless communication systems, regardless of their operating frequencies, utilize antennas of one fashion or another. An antenna transforms AC voltage and current (RF Power) at a given frequency into electromagnetic energy which is then radiated into the atmosphere. The transmitted electromagnetic energy can be shaped and styled depending on the design of the antenna. For example, the total energy can be directed to one or more points or be evenly distributed, e.g., omnidirectional. Moreover, the effective power of the transmission can be doubled, quadrupled or more, depending on antenna design.
It is understood in the wireless communication industry that any wireless system, regardless of the cost expended in the design and fabrication of the associated electronic equipment, will only perform as well as the antenna or antennas to which the system is connected to. Also important is the frequency at which the system operates. Low frequencies and high frequencies will behave differently from each other in the atmosphere. Some frequencies travel through the atmosphere close to the earth's surface following the curvature of the earth over the horizon. Other frequencies travel upward and reflect back to earth off the different layers of the atmosphere, e.g., the troposphere, the ionosphere, the stratosphere. Other frequencies travel in a straight line, i.e., along a "line of sight," and do not bend or reflect. Still other frequencies can penetrate buildings as if they weren't there, while other frequencies will bounce off the surface of buildings and trees or heavily wooded areas.
The personal communication systems (PCS) being introduced to the world are fully digital high frequency systems. In order to handle the high speed data which will be processed, some systems operate at a frequency of about 2 GHz. At this frequency, transmission is along a "line of sight." The antennas required for this type of system must be oriented so that the energy is directed across the surface of the earth, i.e., directed generally tangent to the earth from the antenna site. Antenna sites desiring an omnidirectional pattern for this system typically require the installation of three antennas phased 120 degrees apart from each other and absolutely plumb, e.g., perpendicular to the surface of the earth.
In order to cover a specific geographic region, a large number of antenna sites are necessary. The locations of possible sites include attaching the antennas to existing electric transmission towers which are fixed, machined, steel structures. However, electric utilities are generally reluctant to use electric transmission towers for antenna sites due to safety concerns requiring the power through the electric lines to be turned "off" because of extreme high voltage during installation which normally takes more than sixteen hours depending on available manpower and equipment. In some cases, turning off the power and redirecting the power, i.e., providing a "clearance" can cost thousands of dollars per hour.
Other possible antenna sites include installation of the antennas on wooden utility poles. Installation of antennas to a wooden utility pole typically does not require turning off the power through the electric lines because they may not be present or the voltages are low enough that a clearance is not necessary. However, various problems exist in installing the antennas to wooden utility poles particularly since no two poles are exactly alike. For example, wooden utility poles are typically not installed absolutely perpendicular to the earth, they typically have a taper from the bottom of the pole to the top, and they typically are not straight, i.e., have a curve or bend along their length.
Prior art antenna brackets in use today do not satisfy the demands required for wireless communication systems for easily mounting a plurality of antennas to electric transmission towers or on top of wooden utility poles. In particular, prior art fixed antenna brackets attach to a single antenna thereby requiring three separate fixed brackets and separate installation procedures. Because of the imperfections of wooden utility poles, attaching antennas to a pole via fixed brackets may result in one antenna pointed toward the sky while another is pointed toward the earth. Properly aligning the three antennas requires a high degree of skill by the installer and a great deal of time because of the modifications required to the fixed brackets to overcome the imperfections of the wooden utility pole.
There is, therefore, a need for an adjustable antenna bracket for use in the expanding field of wireless communication which overcomes the above-mentioned drawbacks so that an antenna site having a plurality of antennas can be readily installed with the antennas simultaneously adjusted relative to each other, relative to other antenna sites, and plumb with the earth.